1. Field of the Invention
The present invention relates to an optical fiber bundle having a plurality of optical fibers fixed at end portions thereof disposed and fixed in a sleeve.
2. Description of the Related Art
As a method for forming an optical fiber bundle by fixing end portions of a plurality of optical fibers into a metal-made sleeve, conventionally known are a method of fixing a plurality of optical fibers to a sleeve with a transparent adhesive and a method which comprises inserting assembled optical fibers into a sleeve, fusion-bonding them mutually by heating them and then holding and fixing the resulting optical fiber bundle with a transparent adhesive.
The method of using an adhesive is however accompanied with a problem that the adhesive component penetrated into the core and sheath of the optical fibers deteriorates the optical properties of the optical fibers. In addition, the transparent adhesive colored with the passage of time absorbs from an optical source much heat, which melts and distorts the optical fibers during the long-term use, thereby developing the problem of a deterioration in the optical properties.
As a conventional technique for overcoming the above-described problems, disclosed in Japanese Patent Application Laid-Open No. 62437/1996 is a technique of disposing an elastic material layer made of a heat-resistant rubber elastic material inside of a sleeve, thereby preventing both the dropping-out of an optical fiber bundle from the sleeve and the cross-sectional distortion of the optical fibers upon fusion-bonding by heating. In Japanese Patent Application Laid-Open No. 201927/1994 (U.S. Pat. No. 5,222,180), on the other hand, a technique of using as a assembling tool a rigid sleeve which has a softening temperature at least about 10.degree. C. higher than that of the polymer optical fiber bundle is disclosed.
Since no adhesive is employed in the above-described techniques, they are free from the deterioration in the optical properties of the optical fibers caused by the coloring of an adhesive and are therefore excellent. The technique disclosed in Japanese Patent Application Laid-Open No. 62437/1996 is accompanied with the drawbacks that the workability upon processing is poor and because the optical fiber bundle is fixed to the sleeve through the soft elastic material, adhesion between the sleeve and the optical fiber bundle is insufficient and the fibers happen to bend in the sleeve. In the technique disclosed in Japanese Patent Application Laid-Open No. 201927/1994 (U.S. Pat. No. 5,222,180), the difference in a softening temperature between the polymer optical fiber bundle and rigid sleeve is too large so that the adhesion therebetween is insufficient.